Diffusion tensor imaging of native and degenerated human articular cartilage

The optimal MR acquisition strategy for exponential decay constants estimation

Estimating the relaxation constant of an exponentially decaying signal from experimental MR data is fundamental in diffusion tensor imaging, fractional anisotropy mapping, measurements of transverse relaxation rates and contrast agent uptake. The precision of such measurements depends on the choice of acquisition parameters made at the design stage of the experiments. In this report, chi(2) fitting of multipoint data is used to demonstrate that the most efficient acquisition strategy is a two-point scheme. We also conjecture that the smallest coefficient of variation of the decay constant achievable in any N-point experiment is 3.6 times larger than that in the image intensity obtained by averaging N acquisitions with minimal exponential weighting.

Progressive trypsin digestion and serum inhibition in articular cartilage monitored using high-frequency ultrasound in situ

This study investigated the trypsin digestion and serum inhibition in articular cartilage monitored using high-frequency ultrasound system in situ. Three normal bovine patellae were obtained from a local butcher shop. Four full-thickness cartilage-bone specimens were prepared from the lower medial side of each patella and divided into 4 groups: Group A, B, C and D. Group A was treated as control. The samples from the other three groups were digested by trypsin for 40 minutes and then were immersed for 280 additional minutes in trypsin, physiological saline, or fetal bovine serum (FBS), respectively. It was measured in the M-mode ultrasound images that 30% to 54% of the full-thickness cartilage tissue for all the samples was digested by the 40-minute trypsin digestion. The continuous trypsin digestion depleted almost all proteoglycan (PG) content of the samples of Group B. For Group C, the residual enzyme digestion in saline generated a digestion extension only slightly less than that of Group B. The enzyme digestion in the samples of Group D was relatively quickly (approximately 1 hour) stopped by FBS. The final ultrasound data were compared to histology for assessing the PG depletion. Our findings provide important information of enzyme digestion and inhibition inside articular cartilage. Ultrasound represents a useful visual tool to evaluate the dynamics of models of OA in cartilage specimens in vitro.

Steady-state diffusion imaging for MR in-vivo evaluation of reparative cartilage after matrix-associated autologous chondrocyte transplantation at 3 tesla--preliminary results

OBJECTIVES

To demonstrate the feasibility of time-reversed fast imaging with steady-state precession (FISP) called PSIF for diffusion-weighted imaging of cartilage and cartilage transplants in a clinical study.

MATERIAL AND METHODS

In a cross-sectional study 15 patients underwent MRI using a 3D partially balanced steady-state gradient echo pulse sequence with and without diffusion weighting at two different time points after matrix-associated autologous cartilage transplantation (MACT). Mean diffusion quotients (signal intensity without diffusion-weighting divided by signal intensity with diffusion weighting) within the cartilage transplants were compared to diffusion quotients found in normal cartilage.

RESULTS

The global diffusion quotient found in repair cartilage was significantly higher than diffusion values in normal cartilage (p<0.05). There was a decrease between the earlier and the later time point after surgery.

CONCLUSIONS

In-vivo diffusion-weighted imaging based on the PSIF technique is possible. Our preliminary results show follow-up of cartilage transplant maturation in patients may provide additional information to morphological assessment.

Diffusion-weighted and diffusion tensor imaging for pediatric musculoskeletal disorders

Diffusion-weighted imaging (DWI) is a powerful tool that has recently been applied to evaluate several pediatric musculoskeletal disorders. DWI probes abnormalities of tissue structure by detecting microscopic changes in water mobility that develop when disease alters the organization of normal tissue. DWI provides tissue characterization at a cellular level beyond what is available with other imaging techniques, and can sometimes identify pathology before gross anatomic alterations manifest. These features of early detection and tissue characterization make DWI particularly appealing for probing diseases that affect the musculoskeletal system. This article focuses on the current and future applications of DWI in the musculoskeletal system, with particular attention paid to pediatric disorders. Although most of the applications are experimental, we have emphasized the current state of knowledge and the main research questions that need to be investigated.